1. Field of the Invention
The present invention relates to a driver circuit of a display device, more particularly to a technique for reducing heat generation within a data line driver circuit which drivers a display panel by the dot inversion drive technique.
2. Description of the Related Art
The matrix type display panel, in which pixels are arranged in rows and columns, is one of the most typical display devices. The liquid crystal display panel is a typical matrix display panel. In general, a matrix type display panel is provided with a set of scan lines used for selecting rows of pixels, and a set of data lines fed with data signals having signal levels in accordance with grayscale levels of pixels. Pixels are arranged at respective intersections of the scan lines and data lines.
In general, the inversion drive technique, in which polarities of data signals are inverted at a predetermined time cycle, is used for driving a liquid crystal display panel for avoiding deterioration of liquid crystal material within pixels. In other words, pixels within a liquid crystal display panel are generally driven with alternate-current data signals. Typically, polarities of data signals fed to adjacent pixels are opposite to each other with respect to both of the row direction (the scan line direction) and the column direction (the data line direction). Such inversion drive technique is often called dot inversion drive technique.
International publication brochure No. WO96/16347 discloses a liquid crystal display device adapted to the inversion drive technique. This liquid crystal display device includes a pair of buffers for each display output terminal, one of which outputs a positive data signal and the other outputs a negated data signal. A pair of switches are prepared between the respective buffers and the display output terminal, and the switches are selectively operated to achieve the inversion drive techniques. The drive circuit architecture of the disclosed liquid crystal display device is adapted to not only the dot inversion drive, but also the line inversion drive.
Japanese Laid-Open Patent Application No. Jp-A Heisei 10-62744 discloses another technique for driving a liquid crystal display panel with the dot inversion drive technique. FIG. 1 is a circuit diagram of a drive circuit within a liquid crystal display device, which is dedicated to the dot inversion drive. The drive circuit shown in FIG. 1 drives a pair of data lines with a positive buffer 121 and a negative buffer 122. The positive buffer 121 outputs a data signal with the positive polarity with respect to the standard voltage level, while the negative buffer 122 outputs a data signal with the negative polarity with respect to the standard voltage level. The positive buffer 121 is connected with an odd output terminal S2n-1 through a straight switch 123 and connected with an even output terminal S2n through a cross switch 124. The negative buffer 122 is, on the other hand, connected with the even output terminal S2n through a straight switch 125 and connected with the odd output terminal S2n-1 through a cross switch 126. Additionally, a neutralizing switch 127 is connected between the respective output terminals and a common line 128. In the following description, the switches 123 to 127 and the common line 128 may be referred to as output switch circuit.
The straight switches 123, 125, the cross switches 124, 126, and the neutralizing switch 127 are controlled in response to a polarity signal POL and a latch signal STB. When the latch signal STB is set to the “L” level and the polarity signal POL is set to the “H” level, the straight switches 123 and 125 are turned on, and an odd data line connected with the odd output terminal S2n-1 is driven by the positive buffer 121, while an even data line connected with the even output terminal S2n is driven by the negative buffer 122. When the latch signal STB and the polarity signal POL are both set to the “L” level, the cross switches 124 and 126 are turned on, and the odd data line is driven by the negative buffer 122 while the even data line is driven by the positive buffer 121. When the latch signal STB is set to the “H” level, the straight switches 123, 125, the cross switches 124, 126 are turned off, an the neutralizing switch 127 is turned on, regardless of the state of the polarity signal POL. As thus described, the voltage levels on the respective data lines are neutralized by the neutralizing switch 127 before inversing the polarities of the voltage levels on the respective data lines, to thereby reduce the power consumption necessary for driving the data lines.
The liquid crystal display devices disclosed in the above-mentioned documents are both designed to achieve the inversion drive by selectively turning on the switches provided between the buffers and the display output terminals; however, such configuration suffers from a problem of large heat generation at the switches between the buffers and the display output terminals. In the drive circuit shown in FIG. 1, for example, large currents are flown through the switches 123 to 127 to drive the data lines, and therefore the heat generation is increased as the increase in the on-resistance of the switches 123 to 127. Also, the heat generation at the switches 123 to 127 is undesirably increased, when the capacitance of the data lines is increased to achieve a larger size and a fine resolution of the liquid crystal display panel. The increased heat generation undesirably reduces the lifetime of the data line drive circuit.
One approach for avoiding this problem may be using large-sized transistors as the switches 123 to 127, which effectively reduces the on-resistance of the switches 123 to 127; however, this approach undesirably increases the circuit size.